ATP is one of the substances released from damaged tissues. It activates P2X receptors in primary sensory neurons and contributes to pain and discomfort. The long-term goal of this research is to understand the role of P2X receptors in nociception. In this grant our focus will be to understand the plasticity in P2X receptors following inflammation and nerve injury. We hypothesize that activation of P2X receptors is greatly enhanced under injurious conditions as results of an increase in the activity of protein kinases, interactions with other receptors and changes in expression of P2X receptors. In vivo and in vitro approaches will be used to test this hypothesis. We will (1) determine the effects of ATP on nociceptive behaviors, (2) identify the functional properties of sensory afferents responsive to ATP and quantify the responses of these afferents to ATP, (3) determine the properties of ATP-induced currents and intracellullar Ca 2+ mobiliTation and (4) determine the mechanisms underlying the potentiation of ATP responses by examining the effects of protein kinases and nociceptive mediators, i.e., bradykinin and prostaglandin E2, on ATP-evoked current and Ca 2+ responses and by determining the expression of P2X receptors. Behavioral experiments will be performed on normal, inflamed and nerve injured rats in vivo. Electrophysiological experiments will be performed on skin and DRG-nerve preparations and single DRG neurons isolated from these rats. Membrane currents will be measured with patch electrodes. Single-unit activity will be monitored with extracellular electrodes, intracellular Ca2+ concentrations will be studied using Ca2+ dyes and P2X receptor expression will be examined with Western analyses. These studies should provide a better understanding of the mechanisms underlying the plasticity of P2X receptors under injurious conditions. The information will be essential for developing new strategies for the treatment of chronic pain.